This invention relates to an improved process for preparing a phthalocyanine composition. More specifically, this invention is directed to the reactive formation and treatment of vanadyl phthalocyanine to achieve improved electrophotographic properties.
The formation and development of electrostatic latent images on the imaging surface of photoconducttive members by electrostatic means is well known. Generally, the method involves the formation of an electrostatic latent image on the surface of an electrophotographic plate, referred to in the art as a photoreceptor. This photoreceptor usually comprises a conductive substrate and one or more layers of photoconductive insulating material. A thin barrier layer may be interposed between the substrate and the photoconductive layer in order to prevent undesirable charge injection.
Many different photoconductive members are known, including, for example, a homogeneous layer of a single material such as vitreous selenium, or a composite layered device containing a dispersion of a photoconductive composition. An example of one type of composite photoconductive member is described, for example, in U.S. Pat. No. 3,121,006. The composite photoconductive member of this patent comprises finely divided particles of a photoconductive inorganic compound dispersed in an electrically insulating organic resin binder. The photoconductive inorganic compound usually comprises zinc oxide particles uniformly dispersed in an electrically insulating organic resin binder coated on a paper backing. The binder materials disclosed in this patent comprise a material which is incapable of transporting for any significant distance injected charge carriers generated by the photoconductive particles. The photoconductive particles must therefore be in substantially contiguous particle to particle contact throughout the layer to permit the charge dissipation required for a cyclic operation. The uniform dispersion of photoconductive particles requires a relatively high volume concentration of photoconductor material, usually about 50 percent by volume, in order to obtain sufficient photoconductor particle to particle contact for rapid discharge. Specific binder materials disclosed in this patent include, for example, polycarbonate resins, polyester resins, polyamide resins, and the like.
Also known are photoreceptor materials comprising inorganic or organic materials wherein the charge carrier generating and charge carrier transport functions are accomplished by discrete continguous layers. Layered photoresponsive devices including those comprising separate generating and transport layers are described, for example, in U.S. Pat. No. 4,265,990. Additionally, layered photoreceptor materials are disclosed in the prior art which include an overcoating layer of an electrically insulating polymeric material. Overcoated photoresponsive materials containing a hole injecting layer, overcoated with a hole transport layer, followed by an overcoating of a photogenerating layer, and an outer coating of an insulating organic resin are described, for example, in U.S. Pat. No. 4,251,612. Photogenerating layers disclosed in these patents include, for example, trigonal selenium and phthalocyanines and transport layers including certain diamines. The disclosures of U.S. Pat. Nos. 4,265,990 and 4,251,612 are incorporated herein by reference in their entirety.
Certain phthalocyanine compositions are useful for incorporation into photoresponsive devices to extend the response capability of such devices to include visible light as well as infrared illumination. These photoresponsive devices can be utilized, for example, in conventional electrophotographic copiers as well as in laser printers. Moreover, these photoresponsive devices may comprise single or multilayered members containing photoconductive materials comprising phthalocyanine compositions in a photogenerating layer, between a photogenerating layer and a hole transport layer, or between a photogenerating layer and a supporting substrate.
Vanadyl phthalocyanine has been found to be particularly suitable for photoresponsive devices. Numerous processes are known for preparing and treating vanadyl phthalocyanine. These are described, for example, in U.S. Pat. No. 2,155,038 and U.S. Pat. No. 3,825,422 in which phthalonitrile and vanadium pentoxide reacted in the absence of a solvent. Various other examples are disclosed in U.S. Pat. No. 3,825,422 and U.S. Pat. No. 4,032,339 in which vanadyl phthalocyanine is prepared by utilizing vanadyl trichloride and other co-reactants in the presence of various solvents. The use of vanadium trichloride as a reactant for forming vanadyl phthalocyanine is less desirable because it is a hydrolytically active compound which contributes to instability and the formation of hydrogen chloride.
Phthalocyanines may be treated with sulfuric acid as disclosed, for example, in U.S. Pat. No. 2,155,038; U.S. Pat. No. 3,717,493; U.S. Pat. No. 3,825,422; U.S. Pat. No. 4,032,339; U.S. Pat. No. 4,076,527; British Pat. No. 502,623 (complete specification accepted Mar. 22, 1939) and Japanese Patent Application No. 49-43264, published Nov. 20, 1974.
The particles formed by many of the prior art processes are relatively large and less sensitive to light. Thus, longer exposure times are required which render the materials unsuitable for high speed electrophotographic imaging devices. Moreover, many of the prior art processes involve steps which promote the formation of degradation products which are difficult to remove in subsequent steps and ultimately affect electrical properties of the vanadyl phthalocyanine product. Although treatment with an acid facilitates the formation of smaller particle sizes, difficulties have been encountered achieving very small particle sizes. Moreover, vanadyl phthalocyanine particles cannot simply be physically ground down to the appropriate size because of the tendency of the grinding processes to form particles having very large particle size range distribution including relatively large particles. The classification of ground vanadyl phthalocyanine particles is time consuming and provides a poor yield.
As the art of xerography continues to advance, more stringent standards need to be met by the electrostatographic imaging apparatus to improve performance and to obtain higher quality images. Also desired are layered photoresponsive devices which are more responsive to visible light and/or infrared illumination for certain laser printing applications. As these electrophotographic products become more sophisticated and operate at higher speeds, the operating tolerances become extremely stringent and the predictability of electrical behavior of components can be particularly critical.
While prior art processes for preparing vanadyl phthalocyanine may be suitable for their intended purposes, there continues to be a need for an improved process for preparing vanadyl phthalocyanine having predictable electrical properties.